The panhead was a Harley-Davidson motorcycle engine, so nicknamed because of the distinct shape of the rocker covers. The engine is a two-cylinder, two-valve-per-cylinder, pushrod V-twin. Aluminum cylinder heads for improved cooling and hydraulic tappets were added to the existing bottom end. The engine replaced the Knucklehead engine in 1948 and was manufactured until 1965 when it was replaced by the shovelhead.
As the design of Harley-Davidson engines has evolved through the years, the distinctive shape of the valve covers has allowed Harley enthusiasts to classify an engine simply by looking at the shape of the covers, and the panhead has covers resembling an upside-down pan.
Currently, a number of third-party engine manufacturers produce custom panhead-style engines in a variety of bores, many much larger than the original-design displacements. Each manufacturer includes significant subtle upgrades to the original design to drastically improve the performance and reliability while still providing the original styling and overall engine structure.